How to turn plastic waste into diesel fuel cheaply

[Excalibur]

In the interests of safety, the question has to be asked..
If (for example) 304 stainless was used for the retort vessel, does the applied flame temperature have to be limited to 870°C at the point of contact?

[sunilkm153]

Resistance to oxidation, or scaling, is dependent on the chromium content in the same way as the corrosion resistance is. Most austenitic steels, (304 and 316) with chromium contents of at least 18%, can be used at temperatures up to 870°C. However, be aware that 316 can be prone to cracking.
Grades 309, 310 and 2111HTR (UNS S30815) will withstand even higher temperatures.
Plus the ferritic grade 446 - this has approximately 24% chromium, and can be used to resist scaling at temperatures up to 1100°C.
304/316 = 870 degC
309 = 980
310 = 1035
446 = 1100
2111HR = 1150

The issue is cost of making a vessel of these materials, against how long you get from a Mild steel Vessel and how long it lasts. Mild steel is far cheaper when I was using a vessel for a retort in the earlier days, I decided to stick with mild steel and just replace it, rather than a far greater cost of a SST vessel.

Good explanation by wheels ss 304 is sufficient for retort vessel even professional processors opt for it no need to think about any other option

[Heartburn]

Synopsis available somewhere ?

Hey guys,

Has anybody posted a synopsis of all the parameters discussed here ? I've read the thread and didn't thing of writing everything down as I read.

I want to build a unit with a custom control panel. Building to control panel is a lot of work so If I can save a few hours by not having to go through all the posts a other time it would be very helpful.

Thanks in advance,

hb.

[wheels]

Thank you.
Others recommended are a516/70 and 3cr12 plus vrn400.
Had a collapsed fire wall,made of 6mm mild steel.RETORT made of same material and no problem on inspection.
This machine fired 5 days/ week. Lasted for one year.

Resistance to oxidation, or scaling, is dependent on the chromium content in the same way as the corrosion resistance is. Most austenitic steels, (304 and 316) with chromium contents of at least 18%, can be used at temperatures up to 870°C. However, be aware that 316 can be prone to cracking.
Grades 309, 310 and 2111HTR (UNS S30815) will withstand even higher temperatures.
Plus the ferritic grade 446 - this has approximately 24% chromium, and can be used to resist scaling at temperatures up to 1100°C.
304/316 = 870 degC
309 = 980
310 = 1035
446 = 1100
2111HR = 1150

The issue is cost of making a vessel of these materials, against how long you get from a Mild steel Vessel and how long it lasts. Mild steel is far cheaper when I was using a vessel for a retort in the earlier days, I decided to stick with mild steel and just replace it, rather than a far greater cost of a SST vessel.

[Excalibur]

Rozier,
Good to know your retort held up for some 250+ firings. I'm guessing that the firewall was placed to reduce overheating of the vessel? I suppose you've made the firewall sacrificial?
With 250+ firings you must have learnt quite a lot about what's working well, what's giving problems and found some nice solutions. Are you willing to share any pics or info so the forum community can benefit?
Thanks.

[rozier56]

rozier56

Thank you.
Others recommended are a516/70 and 3cr12 plus vrn400.
Had a collapsed fire wall,made of 6mm mild steel.RETORT made of same material and no problem on inspection.
This machine fired 5 days/ week. Lasted for one year.

[Excalibur]

You need a heat resistant type.
Grade 309 looks like a good candidate. More study required though.
http://www.aksteel.com/pdf/markets_p...data_sheet.pdf
Hope this helps.

[rozier56]

rozier56

Pls remind me why i cant make my retort out of stainless steel?

[Excalibur]

Who's out there??

I'm in the planning stages of a new continuous feed retort/reactor. I want the new plant to be better automated. Basically I'll review everything I've learnt and devise a simple unit. With diesel prices still very low there is no urgency.
Will be be updating the blog with progress.
Thanks!

[wheels]

I have a machine burning waste plastic shreds.When we reach temp of 285*c we produce product of 0.78 on hydrometer.
We increase temp by 1*c and it starts to wax when cooled too 20*c.
Just cant get to the 0.80 on hydrometer to clear as diesel.
Any idea's?

Are there any updates rozier. We are all interested in knowing how you have got on.

For others reading, you will note that often times there are many varied answers given. Many answers seem conflicting. This is because there really are so many variables. Size of Plant, Heat energy input, type of plastic or WMO, speed the Feedstock is processed at, design of reflux, is a catalyst used and what is used as the catalytic medium. There is no one clear definitive answer, unless each and everyone has the exact same plant in every aspect and the exact same Feed Stock. Even commercial plants vary all over the world, as each company tries to find the best most efficient means of producing Fuels from Plastic.

[Excalibur]

The burner is a FBR burner.When i use the 0.50 nozzle the flow rate is 1,8 kg/h,which is 18-22kW /HR.
When we use the 0.75 nozzle the rate is 2.8 kg/h which is 30-33kW /HR.
When i use the 0.75 nozzle my retort heats too quickly and we end up with boil over and make wax.
We have tried the 0.5 nozzle and although the heat up is slow, when we get too retort 390*c and reflux at 322*c we have product that varies between 0.78 and 0.79 on hydro at 20*c.
As we hit the 400*C in retort and 350*c in reflux we get 0.81 at 20*c on hydro.
A 5*C increase in retort will start to give us wax.

I would try reducing the burner heat when your retort goes above 400°C. If that works then it's likely the retort was becoming too lively, frothing up and overwhelming the reflux. Froth is not vapor. It's "bubbles and liquid" .The reflux won't cope and will lose its' ability to separate heavy fractions from light.

[wheels]

The burner is a FBR burner.When i use the 0.50 nozzle the flow rate is 1,8 kg/h,which is 18-22kW /HR.
When we use the 0.75 nozzle the rate is 2.8 kg/h which is 30-33kW /HR.
When i use the 0.75 nozzle my retort heats too quickly and we end up with boil over and make wax.
We have tried the 0.5 nozzle and although the heat up is slow, when we get too retort 390*c and reflux at 322*c we have product that varies between 0.78 and 0.79 on hydro at 20*c.
As we hit the 400*C in retort and 350*c in reflux we get 0.81 at 20*c on hydro.
A 5*C increase in retort will start to give us wax.

You can't be heating evenly. On my first trial plant, I used 2Kw of electric heat for just a few ltrs of Plastic. On my next rest plant, I used 40Kw on 50ltrs of Plastic. The output pipes are 60mm. I struggle to get enough heat even with that. But due to the fact that I need to heat the plastic quickly and get it through the system quickly.
Too much cracking due to excessive time can cause wax.
PE naturally produces Wax.

[wheels]

The retort temp's sit at 325*C to 330*c.
The plastic is ldpe and hdpe pellets and shredded.
We test samples from beginning of production for flammability as we work. paraffin and petrol produced will flame when ignited. Diesel wont burn, so when we achieve this we check hydrometer at 20*c sample and waxing.
My retort size is 310 lt and the reflux 96 lt.
The burner is a 28 kW/HR. This burner is auto controlled to switch on and off at desired temp, either at retort or reflux settings.
It takes me 2,5 hrs to reach desired temps, ie,280*c in reflux column measured at top of column.

The issues with all this are many and varied. This is the problem when ones cross the boundary from a small scale amateur operation to a larger commercial operation, but still using amateur methods. You simply cannot upscale these plants and expect the same results. So many parameters change.
First important question here.....does your retort rotate or do you have any means of stirring the material within the Retort ?
A couple of important points.
28Kw is far from enough heat for 310ltr vessel. You want close to 10 times that.
Plastic is an insulator of Heat. So you need to get that heat right through the Plastic evenly. That is not possible unless the Plastic is stirred or the retort rotated. Otherwise you get plastics overheated where they are closer to the Hot wall of the vessel and not hot enough further on in. The plastics that are heated on the outside then become an even greater insulator to the unmelted on the inside of the mix.
Different plastics naturally produce different weights of Hydrocarbons chains. PE in particular produces Wax. Different plastics also require different heat input. But there are also multitudes of variables that result in what the output stream comprises of. Some commercial operations work with temps as low as 300degC. But some work with Temperatures as high as 900degC. So actual temperature is meaningless unless Time is factored in. Time being the amount of time a Hydrocarbon chain remains within the retort and thus the heat source.
Reflux is purely to re crack long chains that made it out of the Retort. But of long chains do not exist, then re cracking shorter chains is not needed. Heat/time result in the chains braking to ever smaller. More heat and/or longer time the chains are exposed to the heat results in lighter fractions produced.
Commercial plants do not try to produce fuel within the retort itself. They produce a range of Hydrocarbons and then that output is sent to another part of the plant to be cracked into the various fuel outputs they want.
That is all just a brief outline of the complexity of doing this commercially. There is much much more to it than just this even.

[rozier56]

rozier56

The burner is a FBR burner.When i use the 0.50 nozzle the flow rate is 1,8 kg/h,which is 18-22kW /HR.
When we use the 0.75 nozzle the rate is 2.8 kg/h which is 30-33kW /HR.
When i use the 0.75 nozzle my retort heats too quickly and we end up with boil over and make wax.
We have tried the 0.5 nozzle and although the heat up is slow, when we get too retort 390*c and reflux at 322*c we have product that varies between 0.78 and 0.79 on hydro at 20*c.
As we hit the 400*C in retort and 350*c in reflux we get 0.81 at 20*c on hydro.
A 5*C increase in retort will start to give us wax.

[Excalibur]

The retort temperature is extraordinarily low. That's below the temperature at which cracking even begins, 350°C.
The vessel sizes seem reasonable though important is the temperature each vessel can maintain.
I disagree with Wheels with the the view that hotter reflux make lighter product. I believe cooler refux make lighter product because more vapor is able to condense at cooler temperatures, therefore more condensate runs back to the retort. Lighter fractions that resist the condensing effect of the reflux, move downstream and condense as product in the downstream condensers.

Rozier, does the burner use about 2 - 3 liters per hour?
I'd expect very little flow at retort temperatures of 325°C - 330°C, Such flow would be very light fraction and crystal clear.
Are you sure your KW and temperature figures are correct?